Training & Nutrition - Magnesium intake

Hi, I'm going for race 200 km climbing 4 hill in total of over 4000 m (13200 Feet) this race is extremely hard to only the hill’s but it could be hot weather up to 40 deg Celsius (104 F) it is Australia next Sunday (middle of the summer). Could someone tell me what should be the Max intake of magnesium during this race? I’m using Power Gel’s, energy drinks which all have magnesium but I’m thinking to use Endura drink which is very high in magnesium to prevent cramps ( I’m thinking of use this in last 70 Km of race). I just a bit worry to not over do it magnesium could affect the heart rate.

Why not go for an electrolyte pill with sodium and potassium. That is more likely to help you prevent cramps safely than playing with high doses of magnesium.

I wouldn't go much more than the daily recommended intake of magnesium (google RDA of Magnesium) ... over-do the magnesium and your muscles will relax ... ALL your muscles will relax ... including the ones keeping your digestive processes in check. 70 kms is a long, long, long way to go if you've got to make pit stops in the ditch every 15 minutes.

Is this 200K a race or a randonnee (brevet, audax)?

Thanks for this, it is audax but we (6 of us) going to tread this as race this is what we usually do with audax rides (I still rice in veterans).
I always take electrolyte in my drink, but recently someone told me about taking extra magnesium, but I think you are right it could make my muscles to relax. This ride involves 4 hills to climb which I done in the pass so I know what to expect. You can check on this ride viewing below link.
http://www.audax.org.au/alpine-news.asp

Just take the electrolytes supplements you have been using in training. More Mg on race day won't help and might hurt. Sodium is by FAR the most important exercise related electrolyte.

As for muscle relaxation and bowel movements Mg does play a role in both of these things but Machka's explanation of these effects is wrong. Serum Mg levels are tightly regulated as you would die if they went signicantly out of range.

It takes about a month straight of daily Mg supplementation to correct a Mg deficiency as whole body stores of Mg are huge. You are not going to "run out" of Mg during your ride. If you actually are Mg deficient you should take a Mg supplement everyday from now till then, but not race day.

As for Mg relaxing the bowels leading to the runs, that is crap :) . The reason high dose Mg acts as a laxative is because it causes more water to be retained in the gut - the reason for this is, as above, the body won't allow serum Mg levels to go out of range. What occurs is that the body dilutes the Mg in the gut both from fluids you drink and from your body's water stores in order to get the Mg level into the safe range before absorption of the solution. If the Mg dose is too large for dilution and absorption you will take a runny dump and be done with it.

As for Mg relaxing the bowels leading to the runs, that is crap :) . The reason high dose Mg acts as a laxative is because it causes more water to be retained in the gut - the reason for this is, as above, the body won't allow serum Mg levels to go out of range. What occurs is that the body dilutes the Mg in the gut both from fluids you drink and from your body's water stores in order to get the Mg level into the safe range before absorption of the solution. If the Mg dose is too large for dilution and absorption you will take a runny dump and be done with it.

The relaxation of the bowels was just a guess at what happened to me. And ... it took me out of commission one entire morning during which time I alternated between sitting on the toilet, and lying on the floor of the bathroom ... I couldn't get any further from the toilet than that. After about 6 hours, it all subsided and I was able to continue with my day. Since then I haven't even considered going over the RDA of Magnesium ... if anything, I tend to avoid it a bit.

I take HUGE, HUGE, HUGE, HUGE doses of magnesium and it will NOT effect your heart adversely. That's just myth. It will however cause loose bowel movements in excess so you need to get the balance right. I kind of like the Endura electrolyte mix except for the refined sugars in it (lots of fructose, glucose is better for athletes).

I reccomend buying a magnesium suppliment from a chemist or health food store and start off taking 2 to 4 a day now and see how you react. If you get loose bowel movements take fewer but most importantly find out how you will react now and not on race day. Magnesium is a mineral thats good to build up in your body anyway so you have some stores in reserve. Try the Endura too but try it now if your going to and don't wait for the race day.

Regards, Anthony